WO1995025268A1

WO1995025268A1 - Sample testing vessel and method

Info

Publication number: WO1995025268A1
Application number: PCT/GB1995/000567
Authority: WO
Inventors: Diana Margaret Hodgins; Alan Walker Holt
Original assignee: Neotronics Limited
Priority date: 1994-03-16
Filing date: 1995-03-16
Publication date: 1995-09-21
Also published as: AU1897895A; GB9405150D0

Abstract

A testing vessel is described for analysing a sample (40) which is placed in a first compartment (15) that can be purged with a gas, sensors (28) capable of detecting gases, vapours or other volatile materials, e.g. using a semi-conductive polymer and a pair of electrical contacts, are placed in a second compartment (16) that can be independently purged and means (20) is provided for establishing communication between the compartments.

Description

SAMPLE TESTING VESSEL AND METHOD

TECHNICAL BACKGROUND

The present invention relates to a testing vessel for holding a sample during testing thereof by at least one sensor that is capable of detecting gases, vapours or other volatile materials and also to a method of testing such a vessel.

PRIOR ART

International Application No. WO93/03355 describes a vice for detecting gases and volatile materials, the device including several sensors, eacn of which comprises a pair of spaced-apart electrical contacts and a semi-conductive polymer spanning the gap between the contacts; the semi-conductive polymer is capable of inter-reacting with gases and volatile material and. when it so inter-reacts, its conductivity changes. Thus, by measuring the conductivity of the polymer between the electrical contacts of each of these sensors, it is possible to detect the presence of gases and volatile materials. By incorporating different polymers in the various sensors of the device that inter-react in different ways to a gas/volatile material, it is possible to detect a broad range of volatile materials and obtain a set of readings from the various sensors that is characteristic of the composition of the sample concerned.

We have discovered that it is highly advantageous not only to obtain the steady- state conductivity of each sensor after exposure to the atmosphere being tested, but also to measure the conductivity prior to stabilisation of the sensor reading since such early readings give further characteristics of the gases or volatile materials in the atmosphere being sensed. Thus, according to a preferred embodiment, it is desirable to measure the signal from each sensor (or a differential of the signal with time) after a certain period has elapsed following exposure of the sensor to the sample concerned. It is known to take measurements using the device described in WO93/03355 by placing a sample (for example a solid or liquid) in a vessel and placing the sensors in the head space above the sample. However, this gives rise to several problems: firstly, it is difficult to assess the precise time when the sensor is exposed to the volatile material in the head space in order to calculate the time that should elapse before making measurements. Secondly, variations in the ambient atmosphere to which the sensor is exposed prior to exposure to the test sample (for example the humidity of the ambient atmosphere) can affect the signal produced by the sensor on exposure to the test sample. The above factors can produce errors in the signals produced by the sensors during the exposure of the test sample, thereby reducing the reproducibility of the sensor device. The present invention overcomes the above problem. BRIEF DISCLOSURE OF INVENTION

According to the present invention, there is provided a device for holding a sample during testing of it by means of at least one sensor that is capable of detecting gases, vapours or other volatile materials, which sensor is exposed during testing to the atmosphere around the sample, which device comprises a first compartment for holding the said sample. a second compartment for holding said at least one sensor, and means for allowing gaseous communication between the said first and the said second compartments to allow exposure of the at least one sensor to the atmosphere around the sample when desired and for preventing such gaseous communication at other times.

The device may include means for providing a controlled atmosphere in the first and/or second compartment, e.g. means for introducing a gas of known composition (a reference gas) so that the sensor is always exposed, prior to any reading, to a reference gas of known, fixed and ineπ composition. Also, means could be included in the first and/or second compartments (for example a desiccating composition or a humidifier) that establishes a fixed humidity within those compartments, in which case the reference gas could be air of the pre-established humidity. However, it is preferred to purge the second compartment with a gas from an external source (for example a compressed gas bottle) since in that way, it is possible to establish the reference atmosphere in the second compartment quickly, simply and cheaply.

The means providing communication between the first and second compartments could be a simple door that opens (for example by sliding or by pivoting) to establish the desired communication, and closes to prevent such communication. Alternatively, the communication could be established by pumping gas or vapour from the first compartment to the second compartment. A third alternative is to provide a breakable seal between the first and second compartments and to break the seal, e.g. by lowering 3. the sensor head through the seal into the headspace, so as to expose the sensors to the vapour. The readings would start generally when the gaseous communication between the compartments is established, e.g. the seal between the sensor head and the vessel is broken. However they may also be started at a defined time after the communication is established. Optionally, a mixture of these two possibilities may be used.

For the sake of convenience, the first and second compartments may be parts of the same single vessel, but it is not necessary for that to be the case, especially when the atmosphere around the sample is brought into contact with the sensor by means other than natural diffusion, e.g. when the atmosphere in the first compartment is pumped into the second compartment.

The present invention also provides a method of sensing gases and vapours using the vessel.

Although reference has been made herein to the type of sensor described in WO93/03355, the testing device of the present invention can be used in connection with any apparatus for detecting gases, vapours or other volatile materials. BRIEF DESCRIPTION OF DRAWINGS

There will now be described by way of example only, two vessels in accordance with the present invention with reference to the accompanying drawings, in which: Figure 1 shows a schematic cross-section through a first vessel; and Figure 2 shows a schematic cross-section through a second vessel.

DESCRIPTION OF BEST MODE

Referring initially to Figure 1. the vessel comprises an outer wall 10 that may be provided with a heating jacket 12 that maintains the vessel at a fixed temperature (for example 25°C). A lid 14 fits over the vessel 10 and provides a gas-tight seal with the walls of the vessel to enclose a first compartment 15. A second compartment 16 that is enclosed by the lid 14. side walls 18 and a door 20 is also p- ided within the vessel. The door is hinged at 22 and can be kept in a closed position by means of a latch 24.

A sensor head 28 is located within the second compartment 16 and electrical connections (not shown) pass through the lid via a seal (not shown) so that the second compartment 16 is gas-tight when the door 20 is closed. The lid also includes a gas inlet 30, allowing gas to be introduced into the first compartment 15. and a gas outlet 34 for removing gas from this compartment. A similar gas inlet and outlet 36, 38 are provided for introducing and removing gas from the second compartment 16. In order to test a substance containing a volatile material (for example a liquid such as perfume, beer, wine or other drinks or a solid such as foodstuffs, for example crisps), the sample 40 is placed into the first compartment of the vessel 10 which is then closed by lid 14. At this stage, the door 20 between the first and second compartments 15, 16 is closed. The atmosphere within the second compartment is maintained at a known composition by introducing a gas (for example by means of a pump or from a gas bottle) of known composition into inlet 36 and it escapes via outlet 38. When the sensor is not in use. it is possible merely to seal inlets 36 and 38. thereby maintaining the sensor head in the reference gas. However, it is preferred to purge the atmosphere within the second chamber 16 prior to taking a measurement in order to ensure that the atmosphere within that chamber is of a known composition. Likewise the atmosphere within the first compartment can be purged by passing an inset gas, e.g. nitrogen, through it via inlet and outlets 30 and 34.

The head space 42 above the sample 40 is then allowed to reach equilibrium. Once the composition of the gas in the head space 42 has reached a steady state, the door 20 can be opened by releasing latch 24. which may be. for example, mechanical or magnetic, thereby allowing volatile materials in the head space 42 into the second chamber 16. In order to speed up the contact between the vapour from the head space 42 and the sensor head 28. gas may be pumped from the head space through outlet 34 and introduced into the second compartment 16 through inlet 36. I it is desired to purge the two compartments 16 and 32 simultaneously with reference gas, this can be done with the door 20 in an open position (as shown in broken lines) by introducing die reference gas into inlet 36 and venting it through outlet 34 or, conversely, by introducing the reference gas through inlet 30 and withdrawing it through outlet 38.

Alternatively .the reference gas could be pumped into both compartments simultaneously with the seal between them intact. It will be appreciated that any method of establishing gaseous communication between the first compartment 15 and the second compartment 16 can be used instead of the door 20; for example door 20 could be dispensed with and the atmosphere around the sample 40 pumped into the second compartment. The sensor head 28 may be permanently installed within the second compartment 16 (as shown in Figure 1) or it may be introduced through an opening in the lid 14 (not shown).

A second embodiment is shown in Figure 2; the same reference numbers will be used in Figure 2 as were used in Figure 1 to indicate equivalent parts in the two vessels.

In Figure 2, the first compartment 15 is formed by a glass vessel 46 and a stainless steel connector cap 48 that is sealed to the top of the glass vessel 46 by an "O"- ring 52. Gas purging inlet and outlets 30. 34 are included in the cap 48. A sample 40 is shown in the vessel 46.

A second compartment 16 formed partly by stainless steel walls and containing the sensor head 28 is sealed onto the cap 48 by a further "O"-ring 50. A thin impervious plastic breakable film 54 extends across the interface between first and second compartments 15. 16 to provide a gas-tight seal between them.

Gas purge inlets and outlets 36. 38 are provided in the second compartment.

A typical test procedure for the vessel of Figure 2 would be as follows:

1. seal the sensor head 28 within the second compartment by means of film seal 54;

2. place die sample 40 into the vessel 46:

3. purge the vessel 46 for five minutes by passing a known reference gas through inlet and outlet 30. 34;

4. leave the sample 40 to equilibrate into the reference gas for typically 1 - 10 minutes depending on the sample and sample vessel size:

5. whilst the sample is equilibrating, purge the sensor head 28 in the second compartment 16 with the same reference gas via inlet and outlet 36, 38 for typically 1-5 minutes,

6. stop purging the sensor head. 7. expose the sensor head to the headspace 42 above the sample 40 by lowering the sensor head 28 and thereby breaking the seal 54; the sensor head 28 should be exposed to the headspace for the required test period;

8. repeat tests can be carried out on the same sample if required. It has been found that whilst the sample is equilibrating it may be advantageous to include a desiccant or a salt solution or water to maintain the moisture level constant.

This could be included in the sample vessel 46 together with the sample but separate from it. thus only affecting the complex vapour in the headspace 42 by removing or adding free water from the matrix. Wherever possible all parts in contact with the vapour or sample should be ineπ.

Typical materials include glass, stainless steel and PTFE.

With the design of Figures 1 and 2 it is also possible to have a vapour as die sample. In this case the vapour would be pumped straight into the sample vessel via inlet

30 and exhausted out via outlet 34 until the sample vessel is totally saturated with the sample vapour. The inlet and outlet would then both be shut e.g. by valves, the sensor head purged, and then the sensor array exposed to the sample vapour.

By using the vessel of the present invention, it is possible to eliminate several variables in the testing procedure, thereby improving the consistency and reliability of the results obtained.

Claims

1. A device for holding a sample during testing of it by means of at least one sensor that is capable of detecting gases, vapours or other volatile materials, which sensor is exposed during testing to die atmosphere around the sample, which device comprises a first compartment (15) for holding the said sample, a second compartment (16) for holding said at least one sensor (28), and means (20, 50) for allowing gaseous communication between the said first and the said second compartments to allow exposure of the at least one sensor to the atmosphere around the sample when desired and for preventing such gaseous communication at other times.

2. The device of claim 1 that includes means for providing a controlled atmosphere in me second compartment, e.g. means (36, 38) for introducing a gas of known composition (a reference gas) so that the sensor is always exposed, prior to any reading, to a reference gas of known, fixed and inert composition.

3. The device of claim 1 or claim 2 that comprises means in the first and/or second compartment (for example a desiccating composition or a humidifier) that establishes a fixed humidity within that or those compartments.

4. The device of claim 2 wherein the reference gas is air of pre-established humidity.

5. The device of claim any one of claims 1 to 4. wherein the means providing communication between the first and second compartments is a door (20) mat opens (for example by sliding or by pivoting) to establish the desired communication, and closes to prevent such communication.

6. The device of claim any one of claims 1 to 4, wherein die means for allowing gaseous communication between the said first and the said second compartments (15, 16) comprises a pump and wherein die communication is established by pumping gas or vapour from die first compartment to the second compaπment.

7. The device of any one of claims 1 to 4, wherein die means providing communication is a breakable film (54).

8. The device of claim any one of claims 1 to 6, wherein die first and second compartments are part of the same single vessel.

9. A method of analysing complex vapours by means of one or more sensors which comprises placing die sample in a first compaπment (15). placing the at least one sensor in a second compartment (16) sealed from the first compartment, allowing the atmosphere around die sample to equilibrate with vapour from the sample, bringing the vapour into contact with the at least one sensor and taking a reading from die at least one sensor.

10. A method of claim 9. wherein die first and second compartments are part of a device as claimed in any of claims 1 to 8.

11. A mediod of claim 9 or claim 10. which includes a plurality of sensors each comprising a pair of spaced-apart contacts and a semi-conductive polymer spanning die gap between the contacts.